ii66 



HUMAN ANATOMY. 



horn to its lower end. On turning aside the vascular fringe, its relations to this 

 part of the ventricle will be found to be identical with those exhibited in the body 

 of the ventricle, since here, as there, the vascular complex is everywhere covered 

 by the thin layer of reflected ependyma and, therefore, excluded from actual 

 entrance into the ventricular space. Tracing the line of attachment of the reflected 

 ependyma, which alone represents the true ventricular wall closing the crescentic 

 choroidal fissure along the dorso-mesial aspect of the inferior horn, it will be 

 found to be continuous with the thin lateral edge of the fimbria throughout the 

 entire length of this attenuated margin, just as it is connected with the fornix 

 within the body of the ventricle. Passing from this line of attachment (taenia 

 fimbriae) over all the villous projections of the choroid plexus, the reflected 

 ependyma returns to the thicker ventricular wall, which it joins along the mesial 

 border of the roof. Thence the ependyma remains in close contact with the 

 remaining parts of the walls of the inferior horn, all the surfaces of which, including 

 those formed by the hippocampus and the collateral eminence, it covers. From 

 these relations (Fig. 1005) it follows that the fimbria in large part is excluded, 

 as are some other parts of the fornix, from the ventricle, only that portion of its 

 surface which extends from its sharp lateral border to the underlying hippocampus 

 forming, strictly regarded, a part of the ventricular wall. The rounded mesial 

 border and the dorsal surface of the fimbria belong to the free mesial surface of 

 the hemisphere. 



The dentate gyrus (fascia dentata) is part of an atrophic convolution belong- 

 ing to the rhinencephalon (page 1151), and as such belongs systematically to that 



division of the hemisphere. 

 Fig. 1005. 



Choroid plexus 



Caudate nucleus, tail 



Taenia seniicircularis 



Ependyma 

 \ 



Cavity of inferior 

 horn of lateral ^ 

 ventricle 



Since, however, it is closely 

 associated with the struc- 

 tures found within the inferior 

 horn of the lateral ventricle, 

 its description has been de- 

 ferred until this place. The 

 dentate gyrus lies on the 

 mesial surface of the hemi- 

 sphere, but is so hidden be- 

 hind the hippocampal gyrus 

 that it is satisfactorily dis- 

 played only after the over- 

 hanging parts of the thala- 

 mus and cerebral crura are 

 removed. On cutting away 

 these structures and drawing 

 downward the hippocampal 

 gyrus, a narrow band of gray 

 matter, notched and corru- 

 gated by numerous minute transverse furrows, is seen protruding between the free 

 rounded mesial border of the fimbria above and the hippocampal fissure below (Fig. 

 992). This band is the gyrus dentatus. On examining frontal sections passing 

 through the inferior horn of the lateral ventricle (Fig. 1005), the relations of the 

 dentate gyrus will be appreciated. In such preparations the gyrus appears as the 

 free, somewhat thinned off edge of cortical gray matter, which is pushed to the 

 surface just below the choroidal fissure through which the pial tissue invaginates the 

 ventricular wall to gain a seeming entrance to the inferior horn. Between the fimbria, 

 which lies immediately above and parallel with it, and the gyrus a shallow groove, 

 the sulcus fimbrio-dentatus, intervenes, whilst below it is bounded by the remains of 

 the hippocampal or dentate fissure. The latter is no longer an evident furrow, as it 

 was when producing the hippocampus, since it has become closed and almost com- 

 pletely obliterated by the apposition of the bordering cortex. 



Traced forward, the gyrus dentatus gradually leaves the fimbria and passes deeply 

 along the inner side of the uncus in connection with which it ends. The terminal 

 part of the gyrus, somewhat reduced in size, at first bends sharply medially along 



Entrance to 

 choroidal fissure 



Fimbria 

 Fimbrio-denlate 

 fissure 

 Gyrus dentatus 



Hippocampal fissure 

 Alveus 



Hippocampus 

 Gyrus hippocampi 

 Collateral fissure 



Frontal section of part of left hemisphere passing through lower end of 

 inferior horn of lateral ventricle. X 2. 



